Is there a way to get a unique value per dupli group instance?
Using Particles as host for DupliGroup

Thus we can use cool feature of mesh-emitter called From Dupli. This means duplis will inherit location of corresponding space on UV map.


Create emitter mesh and unwrap all faces of emitter as separate islands (avoid overlapping in order to have unique values)
Add PS system, so amount of particles is equal to face count (disable
emit random, even distribution and set particle/face ratio to 1)
Choose Whole group as source for duplicating